The objectives of this proposal are to study the ontogenesis of inhibition in the cortex. Attention will be focused on an intrinsic cortical element, the inhibitory interneuron, and the development of its inhibitory influence on pyramidal cell function. This series of experiments is designed to study in detail the maturation of inhibitory function associated with synaptogenesis during early development. The unique features of the general cortex of the turtle Pseudemys scripta will be exploited in these experiments. The turtle cortex contains only pyramidal cells and stellate interneurons, distributed in three distinct lamina. Preliminary studies have shown that the turtle interneuron exerts powerful control over pyramidal cell function through GABA-mediated inhibitory synapses. The cellular differentiation of the inhibitory interneuron of the turtle, and its target cell, the pyramidal neuron, will be explored. The timetable of development of inhibitory synaptic function will be determined along with a detailed characterization of the postsynaptic inhibitory receptor, its ontogenesis, and topographical distribution through early developmental stages. Methods will include conventional intracellular recording techniques, as well as whole cell patch clamp and single channel membrane patch clamp in order to study the ontogenesis of the GABA receptor/ionophore complex in detail. Since inhibitory control over cortical excitability can play a key role in epileptogenesis, these experiments will form a necessary background for studies of epilepsy in the developing cortex.